1. Field of the Invention
The present invention relates to a signal transmitting method, and more particularly, to a method of transmitting a signal in a wireless communication system using a prescribed frame structure.
2. Discussion of the Related Art
Generally, IEEE 802.16m system is able to support FDD (frequency division duplex) including H-FDD (half-frequency division duplex) mobile station operation and TDD time division duplex) both. The IEEE 802.16m system uses OFDMA (orthogonal frequency division multiplexing access) as a multiple access scheme in DL (downlink) and UL (uplink). Contents for OFDMA parameters are shown in Table 1.
TABLE 1Nominal Channel Bandwidth (MHz)578.751020Over-sampling Factor28/258/78/728/2528/25Sampling Frequency (MHz)5.681011.222.4FFT Size5121024102410242048Sub-Carrier Spacing (kHz)10.9375007.8125009.76562510.93750010.937500Useful Symbol Time Tu (μs)91.429128102.491.42991.429Cyclic PrefixSymbol Time Ts (μs)102.857144115.2102.857102.857(CP)FDDNumber of OFDM4834434848Tg = ⅛ Tusymbols per FrameIdle time (μs)62.85710446.4062.85762.857TDDNumber of OFDM4733424747symbols per FrameTTG + RTG (μs)165.714248161.6165.714165.714Cyclic PrefixSymbol Time Ts (μs)97.143136108.897.14397.143(CP)FDDNumber of OFDM5136455151Tg = 1/16 Tusymbols per FrameIdle time (μs)45.7110410445.7145.71TDDNumber of OFDM5035445050symbols per FrameTTG + RTG (μs)142.853240212.8142.853142.853Cyclic PrefixSymbol Time Ts (μs)114.286[TBD][TBD]114.286114.286(CP)FDDNumber of OFDM43[TBD][TBD]4343Tg = ¼ Tusymbols per FrameIdle time (μs)85.694[TBD][TBD]85.69485.694TDDNumber of OFDM42[TBD][TBD]4242symbols per FrameTTG + RTG (μs)199.98[TBD][TBD]199.98199.98
In the following description, a frame structure of the IEEE 802.16m system is schematically explained.
FIG. 1 is a diagram of a basic frame structure in IEEE 802.16m system.
Referring to FIG. 1, each 20 ms super frame is divided into four 5 ms radio frames equal to each other in size. And, the corresponding super frame starts with a super frame header (SFH). In case of using the same OFDMA parameters of Table 1 within a channel bandwidth selected from 5 MHz, 10 MHz and 20 MHz, each of the 5 ms radio frames is constructed with eight subframes. One subframe can be allocated for downlink or uplink transmission. A first type can be defined as a subframe including 6 OFDMA symbols. A second type can be defined as a subframe including 7 OFDMA symbols. And, a third type can be defined as a subframe including 5 OFDMA symbols.
A basic frame structure, is applicable to FDD including H-FDD mobile-station operation and TDD both. The number of switching points in each radio frame of TDD system is 2. The switching point can be defined according to a change of directionality from downlink to uplink or uplink to downlink.
H-FDD mobile station can be included in FDD system. A frame structure in viewpoint of the H-FDD mobile station is similar to a TDD frame structure. Yet, downlink and uplink transmissions occur in two individual frequency bands. Transmission gaps between downlink and uplink (and vice versa) are requested to switch transmitting and receiving circuits to each other.
FIG. 2 is a diagram for an example of TDD frame having a DL-to-UL ratio set to 5:3.
Referring to FIG. 2, assuming that an OFDMA symbol duration is 102.857 μs and that a CP (cyclic prefix) length is set to a length corresponding to ⅛ of a useful symbol length (Tu), lengths of first and second type subframes are 0.617 ms and 0.514 ms, respectively. A last DL (downlink) subframe SF4 is a subframe of a third type. And, a TTG (transmit transition gap) and an RTG (receive transition gap) are set to 105.714 μs and 60 μs, respectively. According to another numerology, the number of subframes per frame and the number of symbols within a subframe may be different.
FIG. 3 is a diagram for an example of a frame structure in FDD system.
Referring to FIG. 3, a base station supporting FDD system is able to simultaneously support half-duplex mobile station operating with a same RF carrier and a full-duplex mobile station both. A mobile station supporting FDD system should use either H-FDD system or FDD system. All subframes are available for both DL and UL transmissions. The DL and UL transmissions can be discriminated from each other in frequency domain. One super frame is divided into 4 frames. And, one of the frames includes 8 subframes.
FIG. 4 is a diagram for TDD and FDD frame structures with CP length corresponding to 1/16 of a useful symbol length (Tu).
Referring to FIG. 4, a frame of IEEE 802.16m system, which has a CP length corresponding to 1/16 of a useful symbol length (Tu) for channel bandwidths of 5 MHz, 10 MHz and 20 MHz, includes 5 first type subframes and 3 second type subframes in FDD system or includes 6 first type subframes and 2 second type subframes in TDD system.
Assuming that an OFDMA symbol duration is 97.143 μs and that a CP (cyclic prefix) length is set to a length corresponding to 1/16 of a useful symbol length (Tu), lengths of the first and second type subframes are 0.583 ms and 0.680 ms, respectively. And, a TTG (transmit transition gap) and an RTG (receive transition gap) are set to 82.853 μs and 60 μs, respectively. According to another numerology, the number of subframes per frame and the number of symbols within a subframe may be different.
As mentioned in the foregoing description, in the IEEE 802.16m system, OFDMA parameters and frame structures for channel bandwidths of 5 MHz, 10 MHz and 20 MHz are only defined for a case that a CP length is ⅛ Tb and a case that a CP length is 1/16 Tb. Namely, a frame structure for a case that a CP length is ¼ Tb has not been proposed so far.
A frame structure with a CP length of ¼ Tb may cause a problem with a previous frame structure with a CP length of ⅛ or 1/16 Tb that interference is generated from a switching point between downlink and uplink. However, a new frame structure enabling mutual co-existence by solving this problem has not been proposed so far.
In the IEEE 802.16m system, OFDMA parameters and frame structures of ⅛ Tb and 1/16 Tb are defined for 8.75 MHz band only but definition has not been made for ¼ Tb yet. When a frame structure with a CP length of ¼ Tb is used, if an idle interval for TTG/RTG is set in a conventional manner, it may cause a problem that this interval becomes smaller than TTG/RTG of a frame structure with a different CP length (⅛ Tb or 1/16 Tb). Therefore, this problem needs to be solved.